The Cosmogrid Simulation: Statistical Properties of Small Dark Matter Halos (2048-533)

We present the results of the "Cosmogrid" cosmological N-body simulation suites based on the concordance LCDM model. The Cosmogrid simulation was performed in a 30 Mpc box with 2048³ particles. The mass of each particle is 1.28x10^5 Msun, which is sufficient to resolve ultra-faint dwarfs. We found that the halo mass function shows good agreement with the Sheth & Tormen fitting function down to ~10^7 Msun. We have analyzed the spherically averaged density profiles of the three most massive halos which are of galaxy group size and contain at least 170 million particles. The slopes of these density profiles become shallower than -1 at the inner most radius. We also find a clear correlation of halo concentration with mass. The mass dependence of the concentration parameter cannot be expressed by a single power law, however a simple model based on the Press-Schechter theory proposed by Navarro et al. gives reasonable agreement with this dependence. The spin parameter does not show a correlation with the halo mass. The probability distribution functions for both concentration and spin are well fitted by the log-normal distribution for halos with the masses larger than ~10^8 Msun. The subhalo abundance depends on the halo mass. Galaxy-sized halos have 50% more subhalos than ~10^11 Msun halos have. This is snapshot 533 of the 2048³ resolution collection.

我们呈现基于一致性Λ冷暗物质（LCDM）模型的“Cosmogrid”宇宙学N体（N-body）模拟套件的研究结果。本次Cosmogrid模拟在边长为30百万秒差距（Mpc）的立方体计算盒子中完成，共包含2048³个粒子。单个粒子质量为1.28×10^5倍太阳质量（Msun），足以解析超暗矮星系结构。我们发现，暗晕（halo）质量函数与Sheth-Tormen拟合公式在低至~10^7倍太阳质量的范围内均保持良好一致性。我们对三个质量最大的星系群量级暗晕开展了球对称平均密度剖面分析，这三个暗晕均包含至少1.7亿个粒子。在最内侧半径处，这些密度剖面的斜率逐渐变缓至大于-1的水平。我们还发现暗晕浓度与暗晕质量存在显著的相关性。尽管浓度参数的质量依赖关系无法用单一幂律函数描述，但基于Navarro等人提出的Press-Schechter理论构建的简单模型，与该依赖关系能够实现合理吻合。自旋参数与暗晕质量则未表现出明显相关性。对于质量大于~10^8倍太阳质量的暗晕，其浓度和自旋的概率分布函数均可通过对数正态分布得到良好拟合。次晕丰度随暗晕质量发生变化。星系级暗晕的次晕数量比~10^11倍太阳质量的暗晕多50%。本数据集为2048³分辨率模拟集合的第533个快照。